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Results for “Shear Strength”

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PubMed1988

Effect of feed and water withdrawal on shear strength of broiler gastrointestinal tract.

The effects of length of feed (0, 6, 12, 18, and 24 h) and water (with and without) withdrawal and sex of broilers on gastrointestinal (GI) fragility (shear strength) and moisture content were determined. The length of feed withdrawal and sex of broilers had significant (P less than .05) effects on shear strength of various segments of the GI tract. Shear values of GI segments increased with time after feed withdrawal, and values were higher for males than females. Access to water did not affect these results. With the exception of the duodenum, moisture content of GI segments did not differ by sex. Shear values and moisture content of the GI segments were not correlated.

Animals↗

PubMed1992

A comparison of the shear strength of chemically versus electrolytically etched metal retainers.

The recent popularity of acid-etched, resin-bonded retainers (RBR) has initiated improvements in design, technique, and etching. This study compared the shear strength of chemically etched Biobond retainers with electrolytically etched retainers bonded to enamel using identical cement. Shear fracture loads were recorded using Instrom testing for all specimens. The mean fracture load for the electrolytically etched castings was greater than that of the chemically etched castings. Electrolytically etched specimens also recorded the greatest and the least fracture load values. These results indicated that, while there were significant differences between the two groups with greater shear strength values for electrolytic etching, there was also more variation in shear fracture load with electrolytic etching.

Acid Etching, Dental↗

PubMed1996

An in vitro evaluation of the tensile and shear strengths of four adhesives used in orthodontics.

The in vitro shear and tensile strength of four enamel adhesives was investigated. The materials examined were System 1+, Vitrebond, C & B Metabond and Panavia-Ex (original version). The mode of failure of each material was also investigated under a scanning electron microscope. Edgewise mesh-backed brackets were bonded to the buccal surface of extracted premolar teeth and forces applied with an Instron 1011 testing machine. Results indicated that Panavia-Ex (with sandblasted brackets) had the highest tensile strength when compared to the other materials (P < 0.01). Panavia-Ex had the highest shear strength when compared to C & B Metabond (P < 0.05) and to the other materials (P < 0.01). C & B Metabond had the highest shear and tensile strength of the other adhesives (P < 0.01). No significant differences were found for System 1+ when compared to Vitrebond for tensile strength, but System 1+ was stronger for shear strength (P < 0.01). Analysis of failure shows that 50% of the samples failed at the adhesive-enamel interface, 25% failed in a combined mode and the remaining 25% failed either adhesively to metal or cohesively.

Acrylic Resins↗

PubMed1978

Punch shear strength of polycarboxylate cements.

Two general conclusions are drawn which apply to all the four commercial polycarboxylate cements: First, the effect of storage condition upon shear strength was much more pronounced after 24 hours than after 1 hour of storage time; second, the effect of storage condition was most extreme when the specimens were tested free of their matrices. Additionally some specific comparisons between the four products tested can be made based on differences of shear strength within the same experimental condition. The effect of confinement decreased in the following order: Boston greater than Bondal greater than PCA greater than Durelon. Sensitivity to storage conditions decreased in this order: Durelon greater than Bondal greater than PCA greater than Boston. Finally sensitivity to storage times decreased in the order Bondal greater than Durelon greater than Boston greater than PCA.

Acrylic Resins↗

PubMed2001

Mechanical instability and ideal shear strength of transition metal carbides and nitrides.

The ideal shear strength of transition metal carbides and nitrides is calculated with the use of the ab initio pseudopotential density functional method. The microscopic mechanism that limits the ideal strength is studied using full atomic and structural relaxation and the results of electronic structure calculations. It is shown that plasticity in perfect crystals can be triggered by electronic instabilities at finite strains. Our study explicitly demonstrates that the ideal strength in these materials is limited by the elastic instability which is in turn initiated by electronic instabilities. The potential application of alloy hardening due to the onset of instabilities at different strains is also discussed.

Journal Article↗

PubMed2004

Shear strength of core-veneer interface in bi-layered ceramics.

STATEMENT OF PROBLEM: Delamination of veneering porcelain from underlying ceramic substrates has been reported for all-ceramic restorations. Whether this phenomenon is an inherent weakness of the veneering porcelain due to a weak interface between the veneering and the core porcelains, or merely a fracture through the veneering porcelain itself, has not been explored. PURPOSE: The purpose of this study was to investigate the strength of the substructure and veneering porcelain interface in all-ceramic systems. METHODS: The all-ceramic systems tested with their respective veneering porcelains were IPS-Empress2 with Eris (IE), Procera AllCeram with AllCeram (PA), Procera AllZircon with CZR (PZ), and DC-Zircon with Vita D (DC). The veneering porcelain recommended by the manufacturer for each material was fired to the ceramic core. A metal ceramic (MC) combination was tested as a control group. Sixty specimens, 12 for each system and control, were made from 1 master die. A cylinder of veneering porcelain 2.4 mm in diameter was applied using a specially designed aluminum split mold. After firing, the specimens were placed in a mounting jig and subjected to shear force in a universal testing machine. Load was applied at a crosshead speed of 0.50 mm/min until failure. Average shear strengths (MPa) were analyzed with a 1-way analysis of variance and the Tukey test (alpha=.05). The failed specimens were examined microscopically at original magnification x20 to classify the mode of failure as cohesive in the core, cohesive in the veneer, or adhesive at the interface. RESULTS: The mean shear strengths (+/-SD) in MPa were MC control 30.16 +/- 5.88; IE bonded to Eris 30.86 +/- 6.47; PZ bonded to CZR 28.03 +/- 5.03; DC bonded to Vita D 27.90 +/- 4.79; and PA bonded to AllCeram 22.40 +/- 2.40. IE, PZ, and DC were not significantly different from the MC control. Microscopic examination showed that adhesive failure, or complete delamination, did not occur between the compatible ceramic core and veneering materials. Failure primarily occurred near the interface with residual veneering porcelain remaining on the core. IE with Eris exhibited cohesive failure in both the core and the veneer. CONCLUSION: The bond strengths of 3 of the tested all-ceramic materials (IE, PZ, and DC) were not significantly different from the control (MC) group.

Aluminum Oxide↗

PubMed1988

Evaluation of shear strength at the cement-endodontic post interface.

The strength characteristics of the cement-implant interface were evaluated for smooth-tapered, threaded, and porous-surfaced endodontic implants with the use of different cements. Specifically, tensile and torsional shear strengths were measured for zinc phosphate, polycarboxylate, glass-ionomer, silicophosphate, and AH-26 cements. The results indicated superior shear strength characteristics for threaded endodontic implants on axial loading. However, this strength was diminished when torsional forces were applied. Porous-surfaced endodontic implants showed strong resistance to both axial and torsional loading.

Bismuth↗

PubMed1994

Shear strength of a distal rabbit femur during consolidation of an osteotomy fixed with a polylactide expansion plug.

The consolidation of a transverse transcondylar osteotomy of the distal rabbit femur, fixed with a self-reinforced polylactide expansion plug, was studied radiographically and mechanically. The peak shear force was assessed by stressing the osteotomy site to failure. The intact contralateral femur of the same rabbit served as a control. Fifteen rabbits were tested in groups of five animals with follow-up times of 6, 12 or 24 wk after fixation of the osteotomy. The absorbable plug, measuring 4.5 mm in diameter and 30 mm in length, had an expandable distal locking blade system. Thirteen osteotomies showed a radiographically solid bony union. The mean shear strength of the specimens was 3.5 MPa at 6 wk, 3.5 MPa at 12 wk and 4.3 MPa at 24 wk. The mean shear strength of the control distal femora was 3.6 MPa. In conclusion, the fixation properties of the newly developed absorbable expansion plug were deemed satisfactory in this experimental fracture model.

Animals↗

PubMed2002

Dentin shear strength: effect of distance from the pulp.

OBJECTIVE: Dentin structure varies with orientation and location. Ultimate shear strength (USS) has also been found in previous studies to vary with location. The present study further explores this relationship between USS and various locations in coronal dentin as well as distance from the pulp. METHODS: Stick specimens were prepared from coronal dentin located in the center or under cusps of human molar teeth. These were tested in the shear mode at various distances from the pulp. RESULTS: Median values ranged from 52.7 (range 29.0-73.1) MPa near the pulp to 76.7 (range 53.9-104.0) MPa near the dentino-enamel junction. No differences were found among the buccal, central or lingual locations, however, the USS near the pulp was found to be significantly lower. SIGNIFICANCE: The properties of coronal dentin vary with distance from the pulp, which may affect adhesion and other aspects of restorative dentistry.

Anisotropy↗

PubMed1999

Pilot study on the early shear strength of porcelain-dentin bonding using dual-cure cements.

STATEMENT OF PROBLEM: One of the most critical steps of the porcelain restoration technique is cementation. Mechanical stress before the resin cement reaches a certain degree of polymerization can displace or even fracture the restoration. Dual-cure materials are intended to be more effective at early stages of polymerization because they contain both photoinitiator and components for chemically activated reaction. PURPOSE: This study evaluated the early shear strength of bonding between porcelain and dentin, using dual-cure cements. MATERIAL AND METHODS: Sixty nonrestored human molars and premolars were randomly divided in 12 groups. The dual-cure cements tested were Porcelite and Dual. A chemically activated cement was also tested (C&B luting composite). Ceramic pieces, 3 mm high, were etched with hydrofluoric acid, silane-coated, and then bonded to flat dentin surfaces with each of the cements, associated with Optibond adhesive system. Photoactivation was made by using a light unit with 450 mW/cm2. The specimens were stored in water at 37 degrees C. Testing times were 10, 30, 90 minutes, and 7 days (referred to as maximum strength). RESULTS: Both Porcelite and Dual dual-cure cements show statistically similar shear strength for the same time interval. The chemically activated material showed statistically lower values when compared with both dual-cure cements, regardless of the time interval. Results at 7 days were much higher than those obtained at 90 minutes for the 3 cements tested. CONCLUSIONS: Both dual-cure cements tested presented similar results. The bond strength of dual-cure cements to dentin was higher at all time intervals than that obtained for chemically activated material. The high values for the coefficient of variation confirmed the technique-sensitive nature of the porcelain/dentin bonding procedure. Although dual-cure cements reach higher bonding strength values faster than the chemically activated material, it is not recommended to stress the bonding until 90 minutes after cementation, because the strength at that time is much lower than the maximum.

Acid Etching, Dental↗

PubMed1993

The shear strength and the failure mode of plasma-sprayed hydroxyapatite coating to bone: the effect of coating thickness.

Plasma-sprayed hydroxyapatite coated (HAC) 50 and 200 microns thick on Ti-6Al-4V cylinders was transcortically implanted in the femora of canines to evaluate in detail the effect of coating thickness on the pushout shear strength and failure mode examined under scanning electron microscope after the periods of 4, 6, 8, and 12 weeks. The HAC coating exhibited higher shear strength at 50 microns than at 200 microns. Its failure mode was conclusively at or near the HAC-bone interface, and the slight attack of body fluid had not degraded the implant to the extent that failure occurred at the HAC-Ti alloy interface after 12 weeks of observation. For 200 microns-HAC, failure was found at the HAC-bond interface, inside the HAC lamellar splat layer and at the HAC-Ti alloy substrate interface, depending on the period of implantation. It was also deduced that the variation of failure mode of 200 microns-HAC with time could not be accounted for by the attack of body fluid alone; the degradation must be a synergetic adverse result of residual stress in the HAC and the attack of body fluid.

Analysis of Variance↗

PubMed1986

Shear strength of brackets bonded to anterior and posterior teeth.

A study was undertaken to determine the maximum shear strength of brackets bonded to anterior and posterior teeth. Brackets were bonded to two groups comprising 12 incisor and 12 molar teeth. After storage in water at 37 degrees C for 10 days, each bracket was tested to failure in a shear mode in a Instron machine. The mean value for the incisors was 164.3 +/- 35.1 kg/cm2 (16.1 +/- 3.4 MPa) and 115.7 +/- 41.1 kg/cm2 (11 +/- 4.0 MPa) for molars. These values, analyzed in a two-tailed test, were statistically different at the 0.01 level of confidence. It was concluded that differences in etching patterns do not necessarily affect shear bond strength and that the predominantly weak link in the bonding chain was at the bracket/resin interface. The lower values for molar teeth may relate to adaptation of the bracket and nonuniform resin thickness.

Acid Etching, Dental↗

PubMed2004

Measurement of the shear strength of a charge density wave.

We have explored the shear plasticity of charge density waves (CDWs) in NbSe3 samples with cross sections having a single microfabricated thickness step. Shear stresses along the step result from thickness-dependent CDW pinning. For small thickness differences the CDW depins elastically at the volume average depinning field. For large thickness differences the thicker, more weakly pinned side depins first via plastic shear, and shear plasticity contributes substantial dissipation well above the depinning field. A simple model describes the qualitative features of our data and yields a value for the CDW's shear strength of approximately 9.5 x 10(3) Nm(-2). This value is orders of magnitude smaller than the CDW's longitudinal modulus but much larger than corresponding values for flux line lattices, and in part explains the relative coherence of the CDW response.

Journal Article↗

PubMed1981

Tensile and shear strengths of bonded and rebonded orthodontic attachments.

The objective of this study was to investigate the effect of a low-viscosity sealing resin and temperature cycling on the tensile and shear strengths of bonded and rebonded attachments. Eighty extracted noncarious human maxillary central incisors were used. The tensile bond strengths of a chemically activated bonding paste to etched enamel, with and without a low-viscosity sealing resin and with and without 500 temperature cycles between 5 degrees C. and 55 degrees C., were determined. The tensile bond strengths on rebonding were determined on the same teeth in such a way that the rebonded specimens were subjected to the same two variables as the originally bonded teeth. The shear bond and rebond strengths were determined on the remaining forty teeth. The specimens were tested to failure in an Instron machine. The bond strengths were expressed in MN.m-2. Analysis of variance was used to analyze the data. Temperature cycling adversely affected tensile bond and rebond strengths, while the sealing resin had no additional effect on tensile and shear bond and rebond strengths. Tensile versus shear and bond versus rebond strengths for similarly prepared specimens were not significantly different.

Acid Etching, Dental↗

PubMed2006

Precooling of the femoral canal enhances shear strength at the cement-prosthesis interface and reduces the polymerization temperature.

Preheating of the femoral stem in total hip arthroplasty improves the cement-prosthesis bond by decreasing the interfacial porosity. The main concern, however, is the potential thermal osteonecrosis because of an increased polymerization temperature. In this study, the effects of femoral canal precooling on the characteristics of the cement-stem interface were evaluated in an experimental model for three test conditions: precooling of the femoral canal, preheating of the stem (44 degrees C), and a control in which stems were inserted at room temperature without thermal manipulation of the implant, cement, or bone. Compared to the control group, precooling of the femoral canal and preheating of the stem had similar effects on the cement-stem interface, with greater interfacial shear strength and a reduced porosity. Femoral canal precooling also produced a lower temperature at the cement-bone interface. No difference was found in the ultimate compressive strength of bone cement for the three preparation conditions. Based on this laboratory model, precooling of the femoral canal could improve shear strength and porosity at the stem-cement interface, minimize thermal injury, and maintain the mechanical strength of the cement.

Arthroplasty, Replacement, Hip↗

PubMed1991

[Contribution for the method of testing the shearing strength of metal ceramic bonding system].

The shown method of testing the shearing strength of metal ceramic bonding systems has proved in connection with the development of metal ceramic materials and their handling as an efficient technique, which leads to reproducible results with a small dispersion. In divergence from the method of Schmitz and Schulmeyer we use material layers in a bigness, which allow usual laboratory manufacturing techniques and above it the bonding strength of single cera layers can be estimated.

Dental Bonding↗

PubMed2003

Silane treatment effects on glass/resin interfacial shear strengths.

OBJECTIVE: Methacrylic resin-based dental composites normally use a bifunctional silane coupling agent with an intermediary carbon connecting segment to provide the interfacial phase that holds together the organic polymer matrix with the reinforcing inorganic phase. In this study, fiber pull-out tests were used to measure the interfacial bond strength at the fiber-matrix interface. METHODS: Glass fibers (approximately 30 microm diameter, 8 x 10 (-2)m length, MoSci) were silanated using various concentrations (1, 5 and 10%) of either 3-methacryloxypropyl-trimethoxysilane (MPS) or glycidoxypropyltrimethoxy-silane (GPS) in acetone (99.8%). Rubber (poly(butadiene/acrylonitrile), amine terminated, M(w) 5500) molecules were also attached to the fiber surface via GPS molecules. The resin was comprised of a 60/40 mixture of Bis-phenol-A bis-(2-hydroxypropyl)-methacrylate (BisGMA) and tri (ethylene glycol) dimethacrylate (TEGDMA). A bead of resin approximately 2-4 x 10(-3)m in embedded length was placed on the treated fibers and light cured. The load required to pull the fiber out of the resin was converted to shear bond strength. RESULTS: Interfacial shear strengths were greater for silanated specimens compared with unsilanated, and for MPS compared with GPS. The same set of samples soaked in 50:50 (v/v) mixtures of ethanol and distilled water for a period of 1 month showed a decrease in properties. SIGNIFICANCE: A positive correlation was found between the amount of silane on the filler surface and the property loss after soaking. Rubber treatment provided improvement in interfacial strength. 5% MPS samples had the highest strength both in soaked as well as unsoaked samples.

Analysis of Variance↗

PubMed1995

In vitro shear strength of bonded amalgam cores with and without pins.

This study compared the shear bond strength of resin-bonded amalgam with and without pins. The coronal third of 240 embedded posterior teeth was removed to expose a flat, nonretentive surface. Three Minikin pins were placed in the dentin in a triangular pattern 1 mm apart. Amalgam was condensed into a Delrin mold (4.2 mm in diameter and 3 mm in height) positioned over each tooth. The adhesives Amalgam-bond, All-bond, Amalgambond with high-performance additive, Panavia EX, and Panavia with Photobond were the materials used to bond the amalgam to the dentin. Half of the samples were immersed in normal saline solution for 7 days and the others for 30 days. Shear bond strengths were recorded as the maximum load per cross-sectional area of the bonded surface with a testing machine with 1 kN load cell and crosshead speed of 0.5 mm/min. A three-factor analysis of variance and Student-Newman-Keuls test (p = 0.05) identified Amalgambond with high-performance additive as the strongest adhesive in this study. The use of pins with or without adhesives increased the shear strength of amalgam samples significantly more than samples that used adhesives alone.

Analysis of Variance↗